Grader-leveler adapted for trailing by tractors

ABSTRACT

A chassis, adapted to be connected to a farm tractor, supports a blade for grading and levelling; the blade is rotatable with respect to the chassis, and can be fixed in position by engaging tooth-and-detent elements, one of them being respectively fixed to the chassis and the other formed on a turntable which is rotatable with the blade. The tooth-and-detent elements include inclined surfaces, and they are held in engagement by adjustable mechanical, hydraulic, magnetic, or other force means so that, when an obstruction is encountered by the blade which exerts a force on the blade in excess of the holding force, the blade can swivel out of position and thus prevent damage to the graderleveler, or to its pulling tractor.

United States Patent 1 Manor 1 Sept. 23, 1975 [5 GRADER-LEVELER ADAPTEDFOR 2,593,880 4/1952 Heavilim 172/780 TRAILING BY TRACTORS 3,043,0347/1962 Kober 172/780 X 3,716,105 2/1973 Hallam 172/781 X [75] Inventor:Gedalyahu Manor, Haifa, Israel [73] Assignee: Technion Research andDevelopment Primary Examiner-Stephen C. Pellegrino Foundation, Ltd.,Haifa, Israel Attorney, Agent, or FirmFlynn & Frishauf [22] Filed: June26, 1972 211 App]. No.: 266,078 [571 ABSTRACT A chassis, adapted to beconnected to a farm tractor, 30 F A P D t supports a blade for gradingand levelling; the blade is 1 Orelgn pp y a a rotatable with respect tothe chassis, and can be fixed July 4, Israel t. in position g g g toothand detent elements 7 one of them being respectively fixed to thechassis and 2% 172/780 2 172/702 the other formed on a turntable whichis rotatable t i 3/1 with the blade. The tooth-andl-detent elementsinclude 1 1e 0 7/ Z /7 4 inclined surfaces, and they are held inengagement by /4 4 6 7 adjustable mechanical, hydraulic, magnetic, orother 56 R f force means so that, when an obstruction is encoun- 1 eerences Clted tered by the blade which exerts a force on the blade inUNITED STATES PATENTS excess of the holding force, the blade can swivelout of 992,117 5/1911 Dix 172/784 X position and thus prevent damage tothe graderl,247,719 11/1917 Reese 172/781 leveler, or to its pullingtractor. 1,363,454 12/1920 Bullock 172/781 2,089,730 8/1937 Brown et a1.172/796 14 Claims, 7 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of43,907,041

US Patent Sept. 23,1975 Sheet 2 of4 3,907,041

US Patent Sept. 23,1975 Sheet 3 of4 3,907,041

" Fla. 5

US Patent Sept. 23,1975 Sheet 4 of4 3,907,041

GRADER-LEVELER ADAPTED FOR TRAILING BY TRACTORS This invention relatesto an agricultural implement capable of serving both as a grader and asa leveler and adapted to being attached to a farm tractor by athreepoint hitch.

In the relevant art the implement known as a grader consists essentiallyin a heavy, oblong blade of curved cross-section drawn across unevenground while fixedly positioned at an angle between zero degrees and aright angle to the direction of movement, an arrangement which enablesthe implement to cast aside those parts of the soil that protrude abovea certain predetermined level. The implement known as a leveler. on theother hand, consists essentially in a blade similar to that used in thegrader but drawn across the ground while at a right angle to thedirection of motion, with two rigid aprons or side-shields of strongmaterial on either side of the blade preventing the soil being carriedforward during operation from being cast aside, thus using it forfilling out cavities in the path of the implement, the entire operationresulting in a clearly defined strip of land substantially more eventhan prior to the operation.

Several types of both kinds of implement are known to the art: Thefour-wheeled trailed type has the advantage of being simple andrelatively inexpensive, but it is long. heavy and unwieldy especiallywhen taken together with the tractor. The self-propelled motorgrader-leveler has an adjustable blade that may be positioned in the twomanners appropriate to grading and leveling respectively, the bladebeing provided with side aprons required for a successful gradingaction. It is convenient to use. all operations being readily surveyedand manipulated from the drivers seat. but it represents a largeinvestment in an essentially singlepurpose aggregate.

The three-point hitched grader seeks to overcome the drawbacks of theimplements described above by being shorter. the blade being carried ona wheelless frame and fixed to the tractor by a three-point hitch;

This type is relatively inexpensive and its action is continuallycontrollable by hand, but it is inconvenient to use and, due to the lackofa support behind the blade, the results of the operation are of a lowquality.

The three-point fixed-blade leveler seeks to overcome some of thedrawbacks of the last named implement by being provided with a supportbehind the blade. and it is also an inexpensive trailer but asinglepurpose implement.

All the aforementioned machines or attached implements are fitted with ablade fixed. at different angles. to the supporting structure in rigidattachment. The blade and/or the structure are therefore liable to damage whenever the encounters an unsurmountable obstruetion. especially ifthis latter is met by the blade in an off-centre place whereby a bendingmoment is exerted on the structural parts.

It is. therefore. an object of the present invention to provide auniversal leveler and grader which can be trailed by a tractor andconstructed to have, with the tractor. an overall length in the order ofthat of a selfpropellcd grader. or less, and in which the blade can beset at a desired angle with respect to the forward motion of theimplement and yet release when an insurmountable obstacle isencountered.

SUBJECT MATTER OF THE INVENTION:

A combined leveler and grader attachment for a farmtractor, to which itcan be secured, for example, by a three-point hitch is provided, inwhich the blade can be readily set at any angle required for theparticular soil working operation by engaging latch and detent means toadjust the angular position of the blade, and in which a safety deviceis incorporated to release the setting of the blade and prevent damageto the implement due to off-centre overload or a heavy obstruction.

In accordance with a feature of the invention, the combined grader andleveler comprises a base frame or chassis with means preferably athree-point hitch for trailing attachment to a farm tractor and, at itsrear end, means for supporting it on the ground. A supporting frame maybe attached to the chassis by adjustable means so designed as to enableit to be positioned at different distances from, and different anglesto, said chassis; a normally horizontal ring or turntable rotatablyattached over the supporting frame to the chassis; it is provided with aplurality of suitably shaped identical notches or serrations in itsouter rim. A grading and leveling blade is rigidly attached to the saidring or turntable. A positioning and quick-release mechanism. whichincludes of a tooth with converging surfaces of a shape and size adaptedfor engagement with the notches or serrations of the turntable ishingedly or slidingly attached to the supporting frame or the chassis insuch a manner that it can be freely moved in or out of said notches.Mechanical, hydraulic, magnetic or other force means act on the tooth,directly or indirectly, to such an extent that the tooth holds thegrader blade in position under normal working conditions. but can beforced out of the particular notch it is engaged in by the force exertedby an overload on the blade, for example the result of an off-centreobstruction, the lateral force being transmitted from the notch to theinclined contacting surface of the tooth.

In one preferred embodiment of the invention the blade is mounted on arotatable ring with the notches covering a part of its periphery. Ahorizontal pin, the tooth-shaped end of which engages with said notches.is pressed into these by a helical spring the force of which can beadjusted. a handle being provided for disengaging the tooth manually inorder to enable the ring and the attached blade to be turned to thedesired angle.

In another embodiment the notches are provided in the upper or lowersurface of the rim of said rotatable ring. a substantially verticalsliding tooth and pin engaging these notches.

In yet another embodiment the tooth is rigidly connected by a rod to apiston movable in a close-fitting cylinder containing a fluid underpressure forcing the piston and the attached tooth into one of thenotches. means being provided for releasing the fluid pressure upon apredetermined lateral load exerted on the tooth by the inclined side ofthe notch resulting in a proportional axial force on the piston.

In a similar mechanism the tooth is connected to one side of a diaphragmcovering the open end of an otherwise closed pressure vessel. meansbeing provided for filling said vessel with a fluid under pressure andfor releasing this pressure upon a predetermined lateral load beingexerted on the tooth.

In a fourth embodiment the tooth, or its extension, is connected to apermanent magnet, the corresponding armature of which is fastened to thesupporting frame. In normal working the tooth is in engagement with anotch, but when the magnet is separated from the armature through theaction of an obstruction in the path ofthe implement; the tooth isdisengaged.

In the accompanying drawings which illustrate, by way of example,several embodiments of the invention and wherein the same numbers areutilzed to denote identical or similar parts,

FIG. 1 is a vertical section through a tractor-drawn grader-leveler inaccordance with the invention, in which the. blade-positioning device isspring-actuated;

FIG. 2 is a plan view of the implement shown in FIG.

FIG. 3 shows a section through a hydraulically operated positioning andrelease mechanism;

.FIG. 4 is a mechanism similar to that shown in FIG. 3 but actuated bypneumatic pressure;

FIG. 5 shows a positioning mechanism utilizing a permanent magnet andits armature;

FIG. 6 shows the supporting frame and a turntable with a grader bladeaffixed to it as well as a modified positioning mechanism;

FIG. 7 is a plan view of the parts shown in FIG. 6.

Referring now to FIGS. 1 and 2 of the drawings, the gradcr-leveler isattached to a farm tractor l by means of a three-point hitch 2 whichpermits the implement to be lifted off the ground. The implement itselfconsists of a chassis frame 3 built of metal tubes or profiles, itsfront part being adapted for the three-point hitch, its rear partprovided with two backwardly projecting parallel arms 4 which, at theirends, support the swivels of two caster wheels 5.

The front of frame 6, which serves as support for the grader blade. ishingedly attached to the chassis by means of a ball joint 7, while therear end of frame 6 is connected to two substantially verticalturnbuckles 8, an arrangement allowing said rear end of the frame to beraised and lowered by using handwhcels 9. Unequal lengths of the twoturnbuckles result in sideways tilting the frame end of the bladeattached to it. for grading at an angle. Lateral rigidity of the rearend is achieved by the provision of one or two diagonal turnbuckles.

The upper point of the three-point hitch, at the front end of theimplement, is attached to the tractor by means of bars 2, the length ofone of which can be changed at will by turning handwheel 20. By turningthe turnbuckles 8 and simultaneously adjusting handwheel 2a the heightof blade 10 from the ground and its angle of attack can be adjusted.

The blade 10 is curved, and its working edge has been specially treatedto achieve hardness in any suitable manncr known to the art. It isrigidly fastened to a rotatable outer ring or turntable 11 by bars 12.The turntable rotates about a fixed inner ring 13 on a plurality ofsteel balls 14, the outer and inner rings together with the steel ballsforming a large ball bearing. The inner ring 13 is rigidly fastened tothe supporting frame the connections not being shown in the drawingwhile the outer ring is free to rotate unless arrested by a positioningdevice as described in the following:

The outer ring 11 is provided on its outer periphery with a plurality oftrapezoidally shaped notches or serrations 15, which are distributedover the periphery in such a manner that they correspond to apredetermined number of'angles at which the blade is to be positioned inrelation to the direction of travel. The notches 15 are engaged by atooth 16" of trapezoidal cross-section forming the end of a'horizontally positioned pin 16. This pin slidingly passes through ahorizontal cylindrical casing 17 which in turn is rigidly fastened tothe supporting frame 6. Inside the casing a helical spring 18 is fittedround the reduced-diameter rear part of the pin so as to force the tooth16" in the direction of the notches15. The rear part 16' of the pin,which projects out of the casing,is provided with an eye enabling it tobe hingedly attached to a hand lever (not shown) for withdrawing thetooth 16" from the particular notch on outer ring 11 in which it isengaged. When the tooth is thus withdrawn, the blade l0can be adjustedto any desired angle, as, governed by the notches provided.

FIGS. 3, 4 and' 5, illustrate different embodiments of the positioningmechanism.

FIG. 3 shows the application of a hydraulic fluid for holding the tooth16" in its, position. A rod 16 passes centrally through a hydrauliccylinder 17.,the rear end 16' of the rod 16 projecting through thecylinder cover 20, thetoothed end 16" of, the rod 16 emerging from theother end of thecylinder. The tooth in this case by way of example is ofhemispherical shape. The rod 16 is fixedly attached to a piston 19,which tightly fits into the cylinder; and an auxiliary weak spring 18between the cylinder cover 20 and the piston I9 pushes the lattertowards the outer ring 11. Theend 16 of the piston rod 16 projectingbeyond the cylinder cover 20 is hingedly connected to a lever 21, whichpermits the withdrawal of the tooth from a notch on the outer ring llforthe purpose of changing the blade angle.

An oil seal and gland 22 in the cylinder cover 20 prevents the loss ofhydraulic fluid along the piston rod through the bore. The portion ofthe cylinder between the cover 20 and the piston 19 is filled with ahydraulic fluid, which is held under pressure and replenished from aclosed half-filled storage vessel 23. Connection between the storagevessel and the said portion of the cylinder is through two pipes, 24 and40. Pipe 40, which passes from the cylinder to the side of the vessel,is fitted with an adjustable pressure relief valve 25. The other pipe,24, runs from the bottom of the vessel to a check-valve 26, whichprevents the return of fluid from the cylinder to the vessel. Connectionbetween the check valve and the vertical branch of the rising pipe isestablished by a short piece of capillary tube 27 or other suitableflow-restricting means. This reduces the flow from the vessel tothecylinder. The top of the vessel is provided with a pressure gauge 28, anair inlet 29, and a check'valve 30, for setting the pressure in thestorage vessel to the level sufficient for holding the' tooth 16" in thenotch on the outer perimeter of the outer ring 11 which determines theappropriate angle of the blade. Should the grader blade meet a majoroffcentrc obstruction, which would be liable to cause damage to theimplement, the moment created results in a tangential force at theperiphery of the outer ring 11 and on the inclined face of the notch andthe tooth 16".The resultant of that force acts on the fluid in thecylinder and increases its pressure until the relief valve 25 opens andsome fluid spills into the vessel 23. The tooth and the no'tchbecomedisengaged, and the outer ring 11 is free to turn, carrying the attachedblade with it. The obstacle is thus easily cleared. The tooth remains inthe disengaged'position because of the slow pressure buildup between thepiston 19 and cylinder cover 20 assured by the capillary tube (flowrestricting means) 27 in the supply line. On the other hand. thecounter-pressure having ceased, the relief valve 25 has closedagain,'and no fluid-can'enter the cylinder therethrough, so that thetoothwill slip several notches, enabling theblade and the ring to turnas far-asis'necessary to clear the obstacle. 3 l

The positioning and release mechanism shown'in FIG. 4 is similar to thatdescribed-with reference to FIG. 3; however, it uses compressed air anda diaphragm instead of a hydraulic fluid anda piston. The open end ofthe vessel 17 containing the compressed air is closed by a flexiblediaphragm 19 held in position by a threaded ring 31. The elongated stemof tooth 16" is guided in a bush 32 and canbe pulled back by means of alever 21 turning on its fulcrum 33. Compressed air is let into thevessel through inlet 29 and checkwalve 30, a pressure gauge 28indicating the pressure in the system.

The operation of thisembodiment of the invention is similar to that of asubstantially similar mechanism based on a spring-loaded tooth, as the'tooth' will snap back into the adjacent notch when the ring is'turnedby an obstruction, to be pushed out again if the moment has not abated.

The positioning mechanismillustrated in FIG. 5 uses the force of apermanent magnet for keeping the tooth in the notch. The outer ring 11rotates about a fixed inner ring 13 on tapered rollers 14, and thenotches 15 are, by way of example, cut into'the'u'p'per surface of thering. The notches are engaged by the tooth-shaped tapered head ofavertical pin 16 guidedby a bore in the armature 34'0f a permanent'horseshoe magnet 35. The magnet is rigidly connected to the upper part of pin16 by means of an eye-nut 36, which serves as a link with the hand lever21 turning on its fulcrum 33. The armature 34 and the fulcrum 33 arefixedly connected to the inner ring 13 by way of a metal support 37intogral with this ring.

In this mechanism the tooth is kept in its notch as long as magnet andarmature are in close contact with each other. When a lateral force,caused by an offeentre obstruction in the path of the implement forcesthe tooth out of its notch, it lifts the magnet off the armature, theinduction force disappears. and the tooth is free to move wholly out ofthe notch impelled by the lateral force exerted on the side of the toothby the obstacle encountered. The outer ring 11 and the attached bladeare thus permitted to rotate freely. The blade is reset by lifting themagnet with the aid of the hand lever 21.

The grader-leveler shown in FIGS. 6 and 7 differs from that shown partlyin FIGS. 1 and 2 in the suspen sion of the blade. Instead of a rotatableouter ring and a fixed inner ring, a turntable 11' turns about avertical shaft 13, which is fixedly attached to a cross-member 39 of thesupporting frame 6. The periphery of the turntable is provided with aplurality of trapezoidal notches 15, which are engaged by a conformingtooth 16, a positioning mechanism thus being formed. The toothconstitutes the lower extremity of an approximately 8-shaped lever 39,the other end 21 of which is handle-shaped. The lever turns about ahorizontal pin 33 fixedly attached to the supporting frame, while ahelical spring 18 in the vicinity of the handle pulls the handle towardsthe frame and thus the tooth in the direction of the notches. Therelease" mechanism works similarly to the arrangements described withreference to FIGS. 3, 4 or 5, in that an off-centre obstacle pushes thetooth l6 outof the notch, the tooth returning to; or sliding over,:succ'essiv.enotches until the obstacle is cleared. The turntable andthe blade arelset while handle 21 is lifted. w

l The above descriptions are to .be regarded as illustrative examplesonly. Other modifications and alterations, as well as'combinations of-different parts'of the devices described, will readily suggestthemselves to a person skilled in the art without thereby'departing fromthe spirit of the invention described hereinuA possible modification isto replace the rear support'wheels 5, as shown in FIGS. 1 and 2, byafloat or floats of the type used in connection with smoothers.Another-modification would be substitution of these wheels by rollers'orroller packers, whereby these arrangements would carry out theadditional task of seed bed preparation, and the equipment will bechosen accordingly.

In any of the embodiments detachable side-shields or aprons forattachment to the endsof the blade may be supplied for conversion fromgrader'to leveler and vice versa.

I claim:

1. A grader-leveler comprising a chasses (3, 6)'having meansat itsforward end for trailing attachment to a farm tractor (Y) and, at itsrear end, means (5) forsupporting the chassis above ground;

a normally horizontal turntable means "(11), and

means (13) securing the turntable means (11) to the chassis (3,6) whilepermitting selective angular positioning thereof with respect to saidchassis;

a grading and leveling blade (10) secured to the turntable means (ll Iwherein the'improvement comprises 1' quick-release and force overloadmeans (15, 16,17)

locating the turntable means (11) and hence the blade (10) in angularlyadjusted position with respect to the chassis (3, 6) comprising a toothelement (16") and a detent element (15),

one of said elements being secured to the turntable means (11) and theother to the chassis (3, 6), said elements having respectivelyconverging slide surface and being relatively movable for mutuallyreleasable engagement with each other;

and releasable force means located on one of said elements, acting inthe direction of movement on at least one of said elements andconstraining said converging surfaces into engagement to hold the graderblade (10) in selected angular position under normal working conditions,but permit disengagement of said tooth and detent elements by relativesliding movement of said converging surfaces upon disengagcmcnt forcesexerted by an overload on the blade as the result of an obstruction inexcess of the engagement force exerted by said force means, thedisengagement force being transmitted between the converging engagingslide surfaces of said elements.

2. A grader-leveler according to claim l wherein the turntable means 11)is rotatable with respect to said chassis (3, 6) and formed withcircumferential notches (15) forming said detents, the blade (10) isrigidly secured to the turntable means (11), and the tooth element (l6)is supported on the chassis.

3. A grader-leveler according to claim I wherein the tooth element (16")is formed with said converging slide surfaces.

4. A grader-leveler according to claim 1 wherein the turntable means(11) is formed with notches (15) on part of its periphery to providesaid detent element;

and the tooth element (16") comprises a substantially horizontal pin 16)having a tooth-shape-end located to engage said notches (15);

the forcce means comprising a spring l8), acting on the pin (16');

the blade (10) being secured to said turntable means (ll); and a handle(21) for disengaging the. tooth (16") manually in order to enable theturntable means (11) and the attached blade (10) to be turned to adesired angle.

5. A grader-levcler according to claim 1 wherein the turntable means(11) is formed with notches (15) or serrations in a face thereof formingsaid dctcnts;

and the tooth element (16") comprises a movable tooth engaging with thenotches or serrations (l5) and having a direction of movement inessentially vertical direction with respect to the plane of rotation ofthe turntable means.

6. A grader-leveler according to claim 1 wherein the force meanscomprises a piston movable in a close fitting cylinder and containing afluid under pressure, the piston being connected to one of said elementsand forcing the elements together and into engagement;

and means are provided connected to the cylinder for releasing the fluidpressure upon a predetermined load being exerted between the elements bythe inclined side of the respective element and resulting in aproportional force on the piston.

7. A grader-leveler according to claim 1 wherein the force meanscomprises a diaphragm connected at one side thereof to one of theelements, the diaphragm being attached to the open end of an otherwiseclosed pressure vessel;

means for filling said vessel with a fluid under pressure;

- and means for releasing said pressure upon a predetermined load beingexerted between said elements.

8. A grader-leveler according to claim 1 wherein the force meanscomprises permanent magnet means connected to one of said elements andarmature magnet means located to hold said elements in engagement.

9. A grader-leveler according to claim 8 wherein one of said magnetmeans is movable with said tooth element and the other is connected tobe non-rotatable with respect to the chassis.

10. A grader-leveler according to claim 1 wherein the means forsupporting the chassis above ground comprises at least one wheelattached to its rear end.

11. A grader-leveler according to claim 1 wherein a plurality of wheelsare provided, said wheels being directionally self-adjusting casterwheels.

12. A grader-leveler according to claim 1 wherein the means forsupporting the chassis above ground level consist of one or more floatsattached to its rear end.

13. A grader-levelcr according to claim 1 wherein the means forsupporting the chassis above ground level consist of one or more rollersor roller-packers attached to its rear end.

14. A grader-leveler according to claim 1 wherein the blade is rotatableabout a substantially vertical axis which is substantially centrallylocated with respect to the chassis;

and the tooth-and-detent element are located offcentre with respect tosaid axis, the force means retaining said tooth-detent elements inengagement under normal working conditions but permitting disengagementof said elements by lateral forces exerted by an overload of the bladeas a result of off-centre obstructions being encountered by said blade,said lateral disengagement force being transmitted between the inclinedengaging surfaces of

1. A grader-leveler comprising a chasses (3, 6) having means at itsforward end for trailing attachment to a farm tractor (1) and, at itsrear end, means (5) for supporting the chassis above ground; a normallyhorizontal turntable means (11), and means (13) securing the turntablemeans (11) to the chassis (3, 6) while permitting selective angularpositioning thereof with respect to said chassis; a grading and levelingblade (10) secured to the turntable means (11); wherein the improvementcomprises quick-release and force overload means (15, 16, 17) locatingthe turntable means (11) and hence the blade (10) in angularly adjustedposition with respect to the chassis (3, 6) comprising a tooth element(16'''') and a detent element (15), one of said elements being securedto the turntable means (11) and the other to the chassis (3, 6), saidelements having respectively converging slide surface and beingrelatively movable for mutually releasable engagement with each other;and releasable force means located on one of said elements, acting inthe direction of movement on at least one of said elements andconstraining said converging surfaces into engagement to hold the graderblade (10) in selected angular position under normal working conditions,but permit disengagement of said tooth and detent elements by relativesliding movement of said converging surfaces upon disengagement forcesexerted by an overload on the blade as the result of an obstruction inexcess of the engagement force exerted by said force means, thedisengagement force being transmitted between the converging engagingslide surfaces of said elements.
 2. A grader-leveler according to claim1 wherein the turntable means (11) is rotatable with respect to saidchassis (3, 6) and formed with circumferential notches (15) forming saiddetents, the blade (10) is rigidly secured to the turntable means (11),and the tooth element (16'''') is supported on the chassis.
 3. Agrader-leveler according to claim 1 wherein the tooth element (16'''')is formed with said converging slide surfaces.
 4. A grader-leveleraccording to claim 1 wherein the turntable means (11) is formed withnotches (15) on part of its periphery to provide said detent element;and the tooth element (16'''') comprises a substantially horizontal pin(16) having a tooth-shape end located to engage said notches (15); theforece means comprising a spring (18), acting on the pin (16''); theblade (10) being secured to said turntable means (11); and a handle (21)for disengaging the tooth (16'''') manually in order to enable theturntable means (11) and the attached blade (10) to be turned to adesired angle.
 5. A grader-leveler according to claim 1 wherein theturntable means (11) is formed with notches (15) or serrations in a facethereof forming said detents; and the tooth element (16'''') comprises amovable tooth engaging with the notches or serrations (15) and having adirection of movement in essentially vertical direction with respect tothe plane of rotation of the turntable means.
 6. A grader-leveleraccording to claim 1 wherein the force means comprises a piston movablein a close fitting cylinder and containing a fluid under pressure, thepiston being connected to one of said elements and forcing the elementstogether and into engagement; and means are provided connected to thecylinder for releasing the fluid pressure upon a predetermined loadbeing exerted between the elements by the inclined side of therespective element and resulting in a proportional force on the piston.7. A grader-leveler according to claim 1 wherein the force meanscomprises a diaphragm connected at one side thereof to one of theelements, the diaphragm being attached to the open end of an otherwiseclosed pressure vessel; means for filling said vessel with a fluid underpressure; and means for releasing saId pressure upon a predeterminedload being exerted between said elements.
 8. A grader-leveler accordingto claim 1 wherein the force means comprises permanent magnet meansconnected to one of said elements and armature magnet means located tohold said elements in engagement.
 9. A grader-leveler according to claim8 wherein one of said magnet means is movable with said tooth elementand the other is connected to be non-rotatable with respect to thechassis.
 10. A grader-leveler according to claim 1 wherein the means forsupporting the chassis above ground comprises at least one wheelattached to its rear end.
 11. A grader-leveler according to claim 1wherein a plurality of wheels are provided, said wheels beingdirectionally self-adjusting caster wheels.
 12. A grader-leveleraccording to claim 1 wherein the means for supporting the chassis aboveground level consist of one or more floats attached to its rear end. 13.A grader-leveler according to claim 1 wherein the means for supportingthe chassis above ground level consist of one or more rollers orroller-packers attached to its rear end.
 14. A grader-leveler accordingto claim 1 wherein the blade is rotatable about a substantially verticalaxis which is substantially centrally located with respect to thechassis; and the tooth-and-detent element are located off-centre withrespect to said axis, the force means retaining said tooth-detentelements in engagement under normal working conditions but permittingdisengagement of said elements by lateral forces exerted by an overloadof the blade as a result of off-centre obstructions being encountered bysaid blade, said lateral disengagement force being transmitted betweenthe inclined engaging surfaces of said element.